Living Light

Giovanna Fasanelli | VOLUME 32, ISSUE 5

Berry’s bobtail squid cultivate a symbiotic relationship with bacteria … to create light.

When you hear the word ‘squid’, do you think: (a) one of nature’s most intelligent and fascinating designs, which continue to astound scientists around the world; or (b) delicious pan-fried with garlic-lemon butter?

Admittedly, squid is delicious. I would, however, have to challenge even the most ruthless, seafood-guzzling diner to eat a Berry’s bobtail squid (Euprymna berryi). Let’s be honest, Berry’s, which grows no bigger than the size of your thumb, is utterly adorable.

Bobtails are really more cuttlefish than squid, but the group, which comprises some 70 species, is distinct enough to form its own cephalopod order, Sepiolida. Although they inhabit various latitudes in all three of the world’s great ocean basins, the bobtails’s preferred habitat is shallow coastal, reef-rich water, where sandy substrates offer them a superb environment in which to bury themselves during the day. The only chance of finding one of these gorgeous animals is after sunset.

Emerging from the sand under the cover of darkness, the Berry’s bobtail sets out on its nightly quest for unwary prey … an unlucky shrimp here, a careless crab there. But it has its own survival concerns, too, for there are many hungry predators that would consider it a highly agreeable snack.

This cute creature has a few defensive tricks up its sleeve, though, akin to the trickery of fantasy-world creatures – it’s a shapeshifter, with added powers of invisibility and light production.

Wait … light production?

Bobtail squid are recently attracting a lot of scientific attention due to a remarkable association with a light-producing bacterium known as Vibrio fischeri. When the bobtails emerge as hatchlings, they begin sequestering the free-swimming bacteria directly from the seawater, housing them in a special organ within their mantles. In a fascinating system of chemical communication known as ‘quorum sensing’, the bacteria begin producing light when their colony reaches a critical density. This makes perfect sense, as the light produced by a lone bacterium would be insufficient to be visible. Within the confines of the bobtail’s light organ, the densely packed bacteria are triggered into switching on their chemical light production and, in doing so, create a cloak of dim light that camouflages the diminutive killer against the pale glow of light cast by the moon and stars.

By untangling both the intricate relationship of the Berry’s bobtail squid and its bacteria, and the intriguing phenomenon of quorum sensing, scientists hope to better understand the way animal and bacteria cells communicate with one other. This may prove to have far-reaching implications in medicine or military technology.

But should this unbelievable chicanery fail to impress you, there’s more.

If discovered by a predator during the day, Berry can deploy a more traditional camouflage technique using colour-changing chromatophores, which enable it to blend into the background like a ghost. And if this doesn’t work to evade the pursuer, it will shoot out a jet of ink that resembles its own body shape, before slipping away at lightning speed by deploying a water jet.

But, for all their clandestine powers, these remarkable little animals live no longer than a year. Laying several clutches of 200-odd eggs during their short lives, the parents abandon their offspring, leaving them unguarded, but certainly not unarmed.


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